The present invention relates to a novel, improved sealant for joints or cavities. More particularly, the invention is concerned with a thermally expandable sealant comprising a fleece or fabric as the carrier, onto which is applied a coating based on expandable graphite, which coating foams in the event of a fire, and with a process for sealing walls or doors in the event of a fire, using the sealant according to the invention.
Hitherto, for the sealing of joints of fire-protection doors, hydrated alkali metal silicates have been used, these having been applied, in a concentrated form, to sealing strips made of sheet metal (see German Pat. Nos. 1,659,608 and 2,529,550) or of glass fiber fleece or fabric (see German Auslegeschrift No. 1,176,546 and German Auslegeschrift No. 1,169,832) and dried at temperatures below 150.degree. C. Under the action of heat, these alkali metal silicates eliminate steam, as a result of which a frothy but brittle coating is formed as the heat insulator. The disadvantage of such joint-sealing compositions based on silicate is their hygroscopicity and their ready absorption of CO.sub.2, as a result of which moist air impairs their expandability. For this reason, the compositions must be sealed, in as airtight a manner as possible, by means of a lacquer finishing coat or by means of a foil wrapping. Furthermore, in the expanded state they are brittle and sensitive to mechanical stress. The expandability of these silicate compositions is about 1:7 (30 minutes at 200.degree. C.).
British Patent No. 1,497,118 further discloses that fire-protection paint and coating systems may be prepared from expandable graphite which is embedded in a binder system of halogen-containing elastomers and phenol/aldehyde resins. On exposure to heat, such paint systems form loosely bound, foam-like compositions which admittedly have low inherent strength but do have very good heat insulating capacity. The loose structure and low inherent strength make it necessary to use an inorganic silicate-based water-insensitive finishing coat which is also intended to protect the highly porous coke layer, containing expanded graphite, against oxidative attack by the flame gases in the event of a fire.
Surprisingly, it has now been found that a thermally expandable sealant having excellent sealing properties may be prepared if expandable graphite is mixed with certain amounts of polychlorobutadiene, an alkylphenol/formaldehyde resin and optionally aluminum hydroxide, and where appropriate, mineral fibers or stabilizers, and the mixture is applied to a fleece or fabric as the carrier. Such sealants, in the event of a fire, not only offer the advantage of high expandability but also, in contrast to the hitherto customary silicate-based sealants, are also distinguished by good flow and creep, which enables them to flow over edges and corners or flow into angled continuations of the joint which is to be sealed, and thereby achieve a complete seal, without losing the internal cohesion of the composition. Furthermore, the joint sealant according to the invention possesses sufficient strength not to crumble as a result of the fire draught, which is surprising because the previously known compositions based on expanded graphite have had to be protected by a finishing lacquer, causing cohesion, in order to increase their strength, whilst according to the invention a finishing lacquer would be disadvantageous since the material then could not display any flow properties. A further advantage of the material according to the invention is that the expansion process commences rapidly.